Naphtha treating process



June 28, 1960 R. A. WOODLE ETAL 2,943,037

NAPHTHA TREATING PROCESS 2 Sheets-Sheet 1 Filed Jan. 7, 1957 #ETAP June28, 1960 R. A. wooDLE ETAL 2,943,037

NAPHTHA TREATING PRocEss Filed Jan. 7, 1957 2 sheets-sheet 2 UnitedStates Patent O NAPHTHA TREATING PROCESS Robert A. Woodle, Nederland,Tex., John K. McKinley, Poughkeepsie, N.Y., and Roland F. Huhndorlf,Port Arthur, and Claude H. McIntosh, Groves, Tex., as-

l signors Vto Texaco Inc., a corporation of Delaware Filed Jan. 7, 1957,Ser. No. 632,739

3 Claims. (Cl. 20879)v tively low octane number. This is due to-therelatively high proportion of low octane normal paratlins, such asn-pentane,.nhexane, n-heptane,vnoctane and the like in Y jected tocatalytic reforming to produce a reformerellluent having a relativelyhigh octane number. This reformerV efiuent made up of hydrogen, butanes,pentanes and higher molecular weight' hydrocarbons is fractionated andthere are separately recovered therefrom a hydrogen stream, va C, orbutane hydrocarbon stream, a C5-or pentane hydrocarbon stream and aremaining reformate stream. These streams are then suitably treated andblended in accordance with the practice of thisinvensuch Vnaphthas.Because of their relatively lowoctane y numbers light naphthas are notparticularly wellsuited for blending in present day high octane motorfuels wherein an octane number of 100 or greater isdesired. However,v i

since the light naphtha fraction usually comprises ajsubstantial portionof the crude `oil and in order to obtain a.satisfaotory yield of highyoctane motor fuel from Ya given amount of crude oil, upgrading of thelight naphtha fraction therefrom must be accomplished. .Y

A principal object of this invention is to provide an improved lightnaphtha conversion process.

Another object of this invention is to provide a process for theconversion of light petroleum fractions, particularly light petroleumnaphthas Vcontaining vsubstantial amounts of straight chainhydrocarbons, in a plurality of relatively high octane streams suitablefor blending in a high octane motor fuel.

Still another object of this invention is to providea process forupgrading light naphthas havinga boiling range in the range of 40-250 F.and containing a substantial amount of straight chain hydrocarbons, atleast l about 5% by volume, to yield a plurality of relatively Y highoctane hydrocarbon streams.

How these and other objects of this invention mayabe accomplished willbecome apparentfrom the accompanying detailed descriptionl and drawingswhich schematically illustrate an embodiment of the practice of thisinvention and wherein Fig. l is a ilow diagram of a naphtha treatingprocess in accordance with one embodiment of the practice of thisinvention and wherein Fig. 2 graphical- Vly illustrates the advantagesobtainable in the practice of this invention.

In accordance with our invention a light naphtha fraction, such as alight straight run naphtha, a light catalytic reformed naphtha, a lightiluid catalytic cracked naphtha, a lightthermal cracked naphtha, naturalgasoline, or mixtures thereof, is fractionated to separate therefrom arelatively high octane hydrocarbon stream, such as a streaml comprisedessentially or predominantly of isopentane. The remaining naphthafraction, substantially free ofvpentanes, particularly isopentane, isthen subtion to -yield a plurality of hydrocarbon streams having arelatively improved octane number. For example, the remaining reformatestream is fractionated by selective adsorption to separate the straightchain hydrocarbons therefrom, thereby yielding a finished reformatehaving a higher octane number. The separated straight chain hydrocarbonsmay then be recovered and suitably con-l verted, as by isomerization,into a relatively higher octane number stream.

A petroleum naphtha fraction suitable for use in the.

practice of this invention might have an initial boiling point-in therange 40-85 F. and an end point in the range 175-250 F. Further, such alight petroleum fraction must contain both straight chain hydrocarbonsand nonstraight chain hydrocarbons and might have the followingcompositions.

Hydrocarbon typ-e;A Y Percent by volume One treating'step, as indicatedabove, .employed in a combination treating `process of`ourinventionincludes- Y a selective adsorption operation wherein arelatively lhigh boiling portion of a catalytic reformate derived fromthe treatment of 'a light, naphtha fraction in accordance with thepractice of this .invention is treated or contacted withl a solidselective adsorbent which selectively atlso'rbsv straight .chainIhydrocarbonrs'to the substantialexclusion carbons. Non-straight chainhydrocarbons whi'charesu'bl-VV stantiallyunaifected'or'unadsorbed bythespecial selective` adsorbent employed'in the practice ofthis'inventionjin-A clude the isparains andthe lisoolelins suchVasisohexane,

Iisoheptanre, 'isoo'ctane isohexene, risoheptene;.isooctene andV thelike as wellas the naphthenes and aromatic hy-f drocarbons.

Any solid adsorbentA which selectively adsorbsV straigliti chainhydrocarbn's'to the substantial exclusion of non- -straightchain'hy'drocarbons can be employed in the practice of thisir'uient'ion.^ Itis preferred, however, to employ asL the adsorbent`,certain natural or synthetic zeolitesjor.' alumino-silicates,A such asa calcium alumino-silicate,

ucts Company fand designatedtype Y5A molecular svtp-,

The crystals Aof this*particular calcium amiamo-silicate,pI Y Yapparently actuallyV a sodium calcium aluinino-silic'ate,`

have a pore sizeior.' diameter of abotSAn'gstronr f 2,9t3,o1. e 1

vPatented Jnnelzagissp,

apore size suic'ient to admit straight chain hydrocarbons, such as then-paraflins, to the substantial exclusion of the non-straight chainhydrocarbons, such as the napthenic, aromatic, isoolefinic andisoparanic hydrocarbons, e.g., isobutane and higher. This particularselective adsorbent is available in various sizes, such as lAG and lsdiameter pellets as well as in a finely divided powder form, suitablefor employment in a fixed bed, a moving bed or a huidized bed adsorptionprocess.

Other selective adsorbents may be employed in the practice of thisinvention. For example, it is contemplated that adsorbents having theproperty of selectively adsorbing straight chain hydrocarbons to thesubstantial exclusion of non-straight chain hydrocarbons in the mannerof a molecular sieve may be obtained by suitable treatment of variousoxide gels, especially metal oxide gels of the polyvalent amphotericmetal oxides.

Other suitable selective adsorbents are known and include the syntheticand natural zeolites which, when dehydrated, may be described ascrystalline zeolites having a rigid three dimensional anionic networkand having7 interstitial dimensions sufficiently large to adsorbstraight chain hydrocarbons but sufiiciently small to exclude thenon-straight chain hydrocarbons. The naturally occurring zeolite,chabazite, exhibits such desirable properties. Another suitablenaturally occurring zeolite is analcite which, when dehydrated and whenall or part of the sodium is replaced by an alkaline earth metal, suchas calcium, yields a material which may be represented by the lformula(Ca, Na)Al2Si4O12.2H2O and which, after suitable conditioning, willadsorb straight chain hydrocarbons to the substantial exclusion ofnon-straight chain hydrocarbons. Naturallyoccurring, orsyntheticallyprepared pha'colite, grnelinite, hannotome and the like orsuitableY modiiications of these products by ybase.` exchange are alsoapplicable-in the practice of this invention.

-Y Other'solid adsorbents` which.. adsorb `straight chain hydrocarbonssuch as n-paraflins and Yn-olefins to the p substantial exclusion ofnon-straight chain hydrocarbons, including the aromatic andnaphthenic'hydrocarbon's, are known. j

`Referring now to the drawing and in greater detail to Fig. 1 thereofthere is schematically illustrated a flow diagram of one embodimentofthe practice of this invention. A light straight run naphtha boilingin the range 604225 F. is introduced via line 10 into debutanizer 11wherein the butanes or C4 hydrocarbons are removed overhead via line 12.The remaining bottoms portion is `recovered via line 14 and introducedinto depentanizer 1 5A wherein the pentane .or C5 fraction comprisedpredominantly of n-pentane and isopentane 'is recovered overhead vaVline 16. The bottomsfrom depentanizer 15 comprising the relatively highmolecular weight hydrocarbons, parafinic and non-paranic, aswell asstraight chain and non-straight chain hydrocarbons, initially present inthe light straight run naphtha isV recovered via line 1,8 and introducedinto catalytic reformer 19 where they are subjected to catalyticreforming in contact with a suitable catalyst such as aplatinum-containing catalyst, eg., platforming catalyst. Catalyticreformer 19 is operated under such conditions of temperature so as toeffect the isomerizaon and/or dehydrocyclization of the straight chainparafinic hydrocarbons and the nonstraight chain parafiinic hydrocarbonsintroduced thereinto'via line 1d, as well as aromatization ofthenaphthenes. Y

There is recoveredfrom catalytic reformer 19 via line 20 a totalreformer effluent comprising hydrogen, together with al small amount ofnormally gaseous hydrocarbons such as methane and ethane, as well asa C4hydrocarbon fraction: comprising. butane and isobutane, a C5hydrocarbon. fractionl comprising n-pentane and isopentane together withrelatively-high molecular weight reformed hydrocarbons such as'non-straight chain C6, C7 and C8 and higherhydrocarbons, such asisohexane, isoheptane,

isopentane, benzene, toluene, xylenes and the like. The reformereflluent from catalytic reformer 19 is carried via line 20 into gasseparator 21 wherein the normally gaseous portion thereof comprisedsubstantially entirely of hydrogen is removed overhead via line 22. Theremaining liquid reformer effluent passes from separator Z1 via line 24into debutanizer 25 wherein there is recovered overhead via line 26 theC4 hydrocarbon fraction comprising butane and isobutane which is blendedor otherwise admixed with the C4 hydrocarbon fraction obtained initiallyfrom the light straight run naphtha via debutanizer 11 and line 12; Theresulting admixture of the butanes may be separately recovered forblending purposes via line 28.

The bottoms from debutanizer 25 is removed via line 29 and introducedinto depentanizer 30 wherein the pentane or C5 hydrocarbon fractionthereof is recovered and then preferably admixed with the C5 fractionrecovered overhead from depentanizer 15 via line 16 and introduced vialine 32 into deisopentanizer 34 from which isopentane or a portionthereof is recovered overhead via line 35. The remaining bottomsreformer eflluent recovered from depentanizer 3G via line 36 isintroduced into adsorber unit or adsorption zone 38. The remainingreformer effluent introduced into adsorption zone 38 comprises reformedrelatively high molecular weight hydrocarbons, including non-straightchain parainic hydrocarbons such as isohexane, isoheptane, isooctane andthe like as well as the cyclic aromatic hydrocarbons such as benzene,toluene, xylenes together with some unreacted or unconverted straightchain hydrocarbons such as n-hexane, n-heptane, n-octa'ne and the like.l `There is provided within adsorption zone 33 a selective`ads'orbentysuch as Linde type 5A molecular sieve which'lselectively adsorbsstraight chain hydrocarbons to th'e'substantial exclusion ofnon-straight chain hydrocarbons. The selective adsoiption unit oradsorption zone may comprise a fixed bed, a fluidized bed or a niovingbed of selective adsorbent maintained at a suitable temperature, such asa temperature in the range 20G-750 F., to effect selective adsorption ofthe straight chain hydrocarbons from the remaining reformer effluentintroduced thereinto. The adsorption operation is carried out at anyconvenient pressure, such as a pressure in the range 0-500 p.s.i.g.Desirably the temperature and pressure within adsorption zone 38 isadjusted so that the reformer efiluent undergoing fractionation thereinis maintained in' the vapor or gaseous phase. Liquid phase adsorption,although operable, is less preferred.

Following the selective adsorption operation carried out withinselective adsorption unit 38 Athere is recovered therefrom via line 39 afinished reformate or reformed naphtha comprised substantially only ofnon-straight chain hydrocarbons and having an increased octane number ascompared with the light straight run naphtha introduced intothe processvia line 10. The finished reformed naphtha recovered from the processvia line 39 may be used directly as a motor fuel or as a high octaneblending component of a high octane motor fuel. Advantageously, thisfinished reformed naphtha may also be blended with the butanes recoveredfrom debutanizer 11 and de'- butanizer 25 via lines 12 and' 26,respectively.

The straight chain hydrocarbons' adsorbed within the selective adsorbentemployed Within adsorber unit 38 are' desorbed therefrom. In accordancewith one embodiment of the practice of this invention the desorption ofthe adsorbed straight chain hydrocarbons is effected by contacting theselective adsorbent with the gaseous fraction recovered from gasseparator 21 via line 22. As' indicated hereinbefore, this gaseousfraction is composed predominantly of hydrogen. The desorption operationis carried out at arelatively elevated temperature, usuallyr in therange 400 F.-800 F., preferably at a tempera'-4 4J-smania the desorptionoperation is carried out at' a :suitable .temperatureV and pressure'sothat the resulting 'desorbed straight chain hydrocarbons are desorbed orrecovered in the gaseous phase. A suitable desorption temperature is inthe range 30G-800` F. and a pressure in the range 0-500 p.s.i.g. Ifdesired, isothermal and/or isobaric adsorption and desorptionoperationsmay be employed.

compatible wthor otherwiseV chemically inert with respect to thestraight chain hydrocarbons to be desorbed and chemically inert withrespect to the adsorbent employed may be utilized. It is preferred,however, as previously indicated to employ the reformer hydrogen efuentrecovered` from gasA separator 21 via line 22 or another material suchas" av C4 hydrocarbon (butane and/or isobutane) readily separable bydistillation from the resulting straight chain hydrocarbon desorbate.

The desorbed straight chain hydrocarbons are recovered from adsorberunit 38 via line 40. If desired, thetotal desorption eluent comprisingthe desorbed straight chain hydrocarbons and gaseous desorbing medium(hydrogen) is returned via lines 41, 42 and 18 to catalytic reformer 19.When the practice of this invention is carried out in accordance withthis embodiment the straight chain hydrocarbons originally present inthe light straight run naphtha introduced into the process via line 10are substantially completely converted to non'straight chainhydrocarbons, either the corresponding non-straight chain isoparainichydrocarbons and/or the related cyclic aromatic hydrocarbons. f

If desired, the desorption efuent recovered from adsorber unit 38 vialine 40 may beY introduced via line 44 together with the bottoms fromdeisopentanizer 34 comprised predominantly of n-pentane into isomerizer45. As indicated in Fig. l, isomerizer 45, if desired, may

. AEXAMPLE "y i i lighty straight run gasoline was debutanized anddepentanizved to yield a reformer charge stock having an initial boilingpointof 150 F. and an end point of`206 F.Y The APIKgravity of the chargestock was 71.8 and a hydrocarbon-,type analysis of the charge stockshowed that'it contained 3.4% by weight aromatics, 1% by weight olens,72.3% by Weight paraflins and 23.3% by weight naphthenes. The charge'stock had an ASTM research octaneNo., clear, of 65.6, +3 cc. TEL of82.0.

The charge stock was subjected to catalytic reforming (platforming) bycontact under reforming conditions of temperature and pressure with aplatinum-containing catalyst (UOPR-S platforming catalyst). Theresulting reformate was depentanized toyield areformate having an ASTMresearch octane No., clear, of 75.4, +3 cc.

' TEL of92.2 i

be supplied with gaseous hydrogen recovered from gas,v

separate'` isomerizers' (notillustrated). are provided to veifectseparate isomerization ofthe n-pentanes Vand sepa? rateisomerization of the desorbedstraight chain hydrocarbons emanating fromadsorberV unit 38. The isomate or isomerizer effluent issuing fromisomerizer 45 via line 48 maybe I,reintrodlglced intoadsorbervunit'v38pvia line 49 to effect separation ofthe non-straightchain and the straight chainhydrocarbons therein. Further, ifV desired,the resulting isomerizer eiiluent may be'admixed Yor otherfromdeisopentanizer-34 viaV line 35. t

' Blending 'of the isomerizerefluent with the `isopentarie infline 35 is`particularly desirable or suitable when the isomerizer euent iscomprised substantially only of `C54 hydrocarbons such as would be thecase when a separate isomerization facility is provided for then-pentane recovered from deisopentanizer 34.

The following example is illustrative of the practice of this invention.

wise blended-via line 50-with the visopentanes recovered Y Thedepentauized reformate was then subjected to a selectiveadsorptive-separation operation employing a sodium calciumalumino-silicate molecular sieve typeadsorbent (Lindetype'SA molecularsieve) to yield 'a fmished reformate having an ASTM researchv octaneNo., clear, of 88.2, +3 cc. TEL of 99.8.

The straightvchain hydrocarbons separated from the reformate byselective adsorption are advantageously separately treatedY as byisomerization'to improve the octane number thereof. For` example, amixture vof straight chain hydrocarbons lcomparable to the straightchain hydrocarbons separated from the reformate during the aforesaidselectiveadsorption operation having a com? positionof about 23% vbyvolume n-pentane, 56% by volume'n-hexane and 21% by volume .i1-'heptaneand hav- -ing an ASTM researchoctane No., clear,.of 39 was contactedwith" afplatinum.isomerization` catalyst at aV temperature of-aboutf850vFi', at. a pressure of 550 p.s'.i.g. and aspace velocity of .1.v./hr./v.employing a hydrogen recycleratefof; about 4,000 s.c.f. per barrel'ofchargel The resulting isornate consisted `of a mixture of straightchain andfnonestraight'chain hydrocarbons `andhad an ASTM researchoctane No., clear, of about 74.

The V resulting isomate, in `accordancewith one embodiment of thepracticeV of this invention, was then vapor'izedf` and contacted withasolid Vselective adsorbent for the removal ofi-fthe s'traightchainhydrocarbons therefrom under .conditions similar `to those employed inthe treating of the depentanized catalytic reformate. The thusnishedisomate exhibited an ASTM researchoctane f No.2; c1ear,;of"about 82:0;Blending of thenished catalytic reformate and thernished 'isomateV couldthen be carried out to yield a naphtha particularly suitable as amotorfuel. j f

Another mixturelof straight chain hydrocarbons comyparable tothehydrocarbonsdesorbed from thel s olid ,ad-

9i charger-.Contactinsttemperatures and the results'ubtained are `g1enin Table-,I below:

' Table 1" Temperature, 1115....1,1... 920 943 Wt.- PercentRec very(Liquid). ,793.8 81.3 Bromine NoY v f v*20 22 Vol.; PercentAromatics-.'-. 15 `13 ASTM Research OctaneNo k e0. 6 Y57.16 +3 ce.TEL/gal so. 4 so, 2

Other mixtures of straight chain hydrocarbons comparable to the straightchain hydrocarbons recovered during the desorption operation having acomposition of about 23% by volume n-pentane, 56% by volume 7 n-hexaneand 21% byvolumenlheptane and exhibiting an ASTM research octane number,clear, of 39 were contacted with various catalysts -uncierYisomeri'zingeonditions of temperature and at a pressure of about -500p.`s.i'.g., a space velocity of 1.0 v./hr./v. and a hydrogen recyclerate of 4000 s.c.f./bbl. The catalysts, reaction .temperatures and ASTMresearchoctaneY No., clear, of the convertedV products and of thefinished converted products, Le., converted products after having beencon- S -250 VF. and containing pentanes and higher molecular weightparainic-hydrocarbons to separate said pentanes from said high molecularweight parainic hydrocarbons, fractionating said pentanes -to separateisopen- Vtane from n-pentane, recovering the resulting separatedisopentane, subjecting the separated n-pentane to isomerization to yieldan isomerized effluent comprising isopentane, catalytically reformingthe higher molecular weight paraflinic hydrocarbons to yield a reformerefliutacted with adsorbent for the removal of straightchain lo entcomprising hydrogen, C4 hydrocarbons, pentanes and hydrocarbons, are setout in Table II below:

l Table l1 higher molecular weight reformed hydrocarbons, sepa- Temp., Fson 85o 90o Catalyst. Plat Baker Ultra Plat. Baker Ultra Plat. BakerUltra Liq. Rec., Wt. Percent 95. 9 99. 3 90. 1 95.0 99. 0 88. 2 67.6 70.1 72. 7 Converted Product, Octane No 60. 0 51. 0 54.0 75.4 74.0 77. l89. 6 70.0 78. 9 Product Finished by Selective Adsorption, Octane Y No78.0 61.0 72 0 S4 0 82.0 82.6 80.3

P1at.-UOP platformng catalyst. Y Bakcr-Sinclair-Baker RD 150 catalyst.Ultra-Standard of Indiana ultraformlng catalyst.

The foregoing examples illustrate how a light naphtha fractionadvantageously is treated to produce a plurality of upgraded stocksparticularly suitable for blending to produce a high octane motor fuel.

Referring now to Fig. 2 of the invention which graphically illustratesthe advantages of the practice of this invention there is illustratedthe yield-octane relationships of naphtha fractions treated inaccordance with the practicevof this invention. As illustrated in Fig;2V the leaded octane (+3 ccs. TEL) of the finished gasolinerange from99.8 to 104.4. A line correlating' the nshed. gasoline leaded octaneyield data intersected 100 octane (+3 ccs. TEL) at about 55 volumepercent'depentanized gasoline yield basis fresh feed to the catalyticreformer (platformer).

From the data presented hereinabveit isapparent that a depentanizedlight straight run gasoline canV be upgraded to above 100 octane (theresearch +3 cc.. TEL) by catalytic reforming (platforming) andsubsequent iinishing or removal of the straight chain hydrocarbons fromthe depentanized reformate.

It has been shown that from 100 barrels of depentanized light straightrun gasoline the following quantities of liquid materials would beproduced Finished gasoline, ASTM Research Octane N o. -l- 100 4 3 ccs.TEL i Finished gasoline, bbls 55` N-pcntane, bbls. (which can beupgraded to isop'en-` tan Desorbate, bbls. (which can be upgradedY byisonicrization or aromatization to high octanehydrocarbons). Bntane,bbls rately separating said hydrogen, said C4 hydrocarbons and saidpentane from said reformer eiiluent, separately recovering the resultingseparated C4 hydrocarbons, subjecting the resulting separated pentanesto fractionation to separate isopentane from n-pentane, blending thethusseparated isopentane with the aforesaid previously separatedisopentane and blending the thus-separated npentane with the aforesaidseparated n-pentane prior to isomerization, subjecting the remainingreformer effluent ,to contact with a solid molecular sievealumina-silicate selective adsorbent which selectively adsorbs straightchain hydrocarbons to the substantial exclusionof nonstraight chainhydrocarbons, said contacting operation being carried out at atemperature in the range ZOO-750 F. and at a pressure in the range of0-500 p.s'.i.g. and under conditions Such that said reformer effluent isin the gaseous phase, recovering from the aforesaid selective adsorptionoperation a first hydrocarbon stream substantially free of straightchain hydrocarbons and desorbing the adsorbed straight chainhydrocarbons from said selective adsorbent by contacting said absorbentwith gaseous aforesaid separated C4 hydrocarbons at a temperature in therange 40G-800 F. and at a pressure `in the range 0-500 p.s.i.g., saiddesorption temperature being 50-250 degrees Fahrenheit greater than theaforesaid ad# `sorptiontemperature and such that the resulting desorbedstraight chain hydrocarbons are in the gaseous'phase.

2. A process in accordance with claim 1 wherein said straight chainhydrocarbons desorbed from saidselec'- tive adsorbent by contact withsaid C4 hydrocarbon are recycled to the aforesaid catalytic reformingoperation.

3. A process in accordance With claim 1 wherein said straight chainhydrocarbons desorbed lfrom said`selective adsorbent are isomerized inthe aforesaid isomerizaton operation.

References Cited in the iile of this patent UNITED STATES PATENTS2,425,535. YI-Iibshman Aug. 12, '1947 '2,442,19l Black May 25 19482,443,607 Evering June 22, l1948 :2,818,449 Christensen et al. Dec. 3l,1.957 2,818,455 Ballard et a1. '-..,Dec. 3.1, 1957

1. A PROCESS FOR UPGRADING A LIGHT NAPHTHA FRACTION INTO A PLURALITY OFRELATIVELY HIGH OCTANE HYDROCARBON STREAMS WHICH COMPRISES FRACTIONATINGA LIGHT NAPHTHA PETROLEUM FRACTION HAVING A BOILING RANGE IN THE RANGE40-250*F. AND CONTAINING PENTANES AND HIGHER MOLECULAR WEIGHT PARAFFINICHYDROCARBONS TO SEPARATE SAID PENTANES FROM SAID HIGH MOLECULAR WEIGHTPARAFFINIC HYDROCARBONS, FRACTIONATING SAID PENTANES TO SEPARATEISOPENTANE FROM N-PENTANE, RECOVERING THE RESULTING SEPARATEDISOPENTANE, SUBJECTING THE SEPARATED N-PENTANE TO ISOMERIZATION TO YIELDAN ISOMERIZED EFFLUENT COMPRISING ISOPENTANE, CATALYTICALLY REFORMINGTHE HIGHER MOLECULAR WEIGHT PARAFFINIC HYDROCARBONS TO YIELD A REFORMEREFFLUENT COMPRISING HYDROGEN, C4 HYDROCARBONS, PENTANES AND HIGHERMOLECULAR WEIGHT REFORMED HYDROCARBONS, SEPARATELY SEPARATING SAIDHYDROGEN, SAID C4 HYDROCARBONS AND SAID PENTANE FROM SAID REFORMEREFFLUENT, SEPARATELY RECOVERING THE RESULTING SEPARATED C4 HYDROCARBONS,SUBJECTING THE RESULTING SEPARATED PENTANES TO FRACTIONATION TO SEPARATEISOPENTANE FROM N-PENTANE, BLENDING THE THUSSEPARATED ISOPENTANE WITHTHE AFORESAID PREVIOUSLY SEPARATED ISOPENTANE AND BLENDING THETHUS-SEPARATED NPENTANE WITH THE AFORESAID SEPARATED N-PENTANE PRIOR TOISOMERIZATION, SUBJECTING THE REMAINING REFORMER EFFLUENT TO CONTACTWITH A SOLID MOLECULAR SIEVE ALUMINA-SILICATE SELECTIVE ADSORBENT WHICHSELECTIVELY ADSORBS STRAIGHT CHAIN HYDROCARBONS TO THE SUBSTANTIALEXCLUSION OF NONSTRAIGHT CHAIN HYDROCARBONS, SAID CONTACTING OPERATIONBEING CARRIED OUT AT A TEMPERATURE IN THE RANGE 200-750* F. AND AT APRESSURE IN THE RANGE OF 0-500 P.S.I.G. AND UNDER CONDITIONS SUCH THATSAID REFORMER EFFLUENT IS IN THE GASEOUS PHASE, RECOVERING FROM THEAFORESAID SELECTIVE ADSORPTION OPERATION A FIRST HYDROCARBON STREAMSUBSTANTIALLY FREE OF STRAIGHT CHAIN HYDROCARBONS AND DESORBING THEADSORBED STRAIGHT CHAIN HYDROCARBONS FROM SAID SELECTIVE ADSORBENT BYCONTACTING SAID ABSORBENT WITH GASEOUS AFORESAID SEPARATED C4HYDROCARBONS AT A TEMPERATURE IN THE RANGE 400-800*F. AND AT A PRESSUREIN THE RANGE 0-500 P.S.I.G., SAID DESORPTION TEMPERATURE BEING 50-250DEGREES FAHRENHEIT GREATER THAN THE AFORESAID ADSORPTION TEMPERATURE ANDSUCH THAT THE RESULTING DESORBED STRAIGHT CHAIN HYDROCARBONS ARE IN THEGASEOUS PHASE.